1. Field of the Invention
This application is related to communications systems and more particularly to integrated circuit transceivers of communications systems.
2. Description of the Related Art
In general, a transceiver is a device that includes both a transmitter and a receiver in a single housing. In a typical transceiver application, power levels of transmitted signals are substantially greater than power levels of received signals at the transceiver terminal(s). Transmit power amplifier circuits are designed to handle relatively large voltage swings. In contrast, typical receiver circuits are designed to accept lower-power signal levels and a substantial amount of the input voltage is applied across gate-source terminals of devices of the receiver circuit. If the transmitter applies a high-voltage transmit signal to a shared transmit/receive terminal connected to a transmitter power amplifier and a receiver amplifier, those high voltage transmit signals will be applied across the gate-source terminals of devices in the receiver circuits and may damage those receiver input devices.
To reduce or eliminate damage to the receiver circuit from high-voltage transmit signals, a typical transceiver includes a transmit/receive switch that selects whether a transmit path or a receive path is operatively coupled to the terminal. The switch may be included as part of the integrated circuit transceiver or external to the integrated circuit transceiver. Implementations of a transmit/receive switch in series with a transmitter power amplifier can result in significant resistive power loss or the switch itself may be susceptible to damage from high voltage transmit signals. Implementations of a transmit/receive selector switch in series only with a receiver path (e.g., low-noise amplifier) may be better-tolerated by the system, but also may increase a noise figure of the system. To be well-tolerated by the system, a transmit/receive switch coupled in series with a receiver path should introduce only relatively low losses and relatively low capacitance, while being able to handle large voltage swings at its input.
In some applications, e.g., a Multimedia over Coax, (MoCA) application, signals may have high peak-to-average signal ratios, e.g., worst-case voltage swings of approximately 0V to two times the supply voltage (2×VDD), although average voltages are substantially lower. Conventional techniques used to implement a low-loss, high-voltage switch are insufficient to handle large peak voltages that result from signals having high peak-to-average signal ratios. Accordingly, new techniques for implementing a transmit/receive switch are desired.